Thanks, Jur! My partner put in Mr Tuffy liners after her first flat, then immediately got another. Our LBS/Brompton dealer said the liner was what caused the flat and said they didn't suggest using them on 16" wheels. But that's an interesting idea to sand the edges. I just might have to give it a try! I otherwise adore the Kojaks--they're so fast and smooth compared to the Marathons.